By Richard Vaughn, Product Engineer
Bosch Rexroth Corporation–Project Management Dept.
In a short time, mechatronics has evolved into a universally accepted engineering concept. It integrates mechanics with electronics – and with engineering itself. The result is expanded technological capabilities and assembly-line successes like the Cartesian multi-axis robot. Because it enables more flexible automated production, users can precisely control parameters such as weight, speed, reach, and work envelope. That is why mechatronics can be the answer to a variety of design challenges.
Mechatronics enables the development of creative designs that extend the capabilities of existing robotics and controls to new levels.
But obtaining the right answers requires asking the right questions – from the very first stage of a design. A mechatronics approach is a 3-stage ongoing process:
—Design – configure the system to accomplish a specific task.
—Integration – determine how components work together.
—Implementation – achieve optimum value in daily operations, and prepare for future changes.
As an example, consider the parameters involved in an application such as pin insertion in automobile underbodies traveling on an assembly line. Proper design begins with the determination of mathematical factors such as payload, travel distance, desired speed, and axes size. Then there are questions of machine control, motor size to deliver proper speed and torque, and even the operator HMI. There is also the key question of how much it all will cost.
The design of a mechatronics system requires a multidisciplinary focus — to root out potential difficulties before they grow into time-consuming, costly and distracting problems.
Here are a few specific mechatronics challenges—and some tips for handling them.
Keep envelope restrictions in mind. Consider work envelope restrictions including walls, supports, and safety barriers to avoid physical interference. The difference between length of a module and length of stroke is also crucial, especially when selecting linear actuators. A rodless actuator’s “dead length” means the actuator’s stroke is shorter than the apparent length of the cylinder. The best approach is to use a 3D simulation, rather than reconfigure system elements later in the project.
Find a proper protocol. Approach the marriage of controls and drives from different sources cautiously – it can lead to problems, especially when using off-the-shelf protocols such as PROFIBUS, DeviceNet or Ethernet. Some off-the-shelf protocols, such as Bosch Rexroth’s IndraControl components, can communicate with many proprietary controllers, but this may not be true of all protocols. Problems may arise if a controller running DeviceNet is added to a platform running PROFIBUS. Similarly, if your plant runs Ethernet, you may not be able to “plug in” a component from any vendor. During the specification phase, you should ensure that compatible off-the-shelf control systems are available for expansion or reconfiguration.
Consider the implications of specifications. Specifications can have powerful, difficult-to-foresee implications for mechatronics. For example, a 480 V 3-phase motor may be ideal for a servo application, but not if your drive amplifier is only capable of 220 V – which may require retrofitting a transformer. A change from Class 1000 to Class 100 semiconductor production clean room conditions may require third party specification.
Build in cable management. Often, this is the last challenge addressed, leading to last-minute scrambles to avoid interference with motion and parts pickup. Rather, cable management for a gantry pick-and-place application should be one of the first factors considered. A program such as Bosch Rexroth’s camoLINE can offer predefined cable management and 3D modeling, letting you “drop in” components to ensure all components work cleanly together.
Cable management is an important and often overlooked consideration during mechatronic system design.
Find the right tool for the job. An application that requires complex interpolative motion, such as cutting or gluing circular seals on catalytic converters, requires an interpolative motion controller and device. Attempts to adapt point-to-point controllers for these applications can be time-intensive and deliver inadequate precision. The best approach is to determine the circular interpolation path and identify the needed controller performance; that in turn will guide the selection of drives, power requirements, I/O and other elements to achieve that performance.
Following some basic tips like these can help avoid common – and costly – problems like either over engineering and over sizing machines (resulting in heavy-duty capabilities that are rarely if ever used) or under sizing machines (not accounting for occasional increases in payload or run speed).
Either situation can unnecessarily increase automation costs, which might discourage implementation of mechatronics – another reason why asking detailed questions is essential.
Mechatronics is clearly a cross-disciplinary science, requiring expertise in mechanical and electrical engineering as well as electronics and computers. But few have a background in all these disciplines. Those with expertise in one particular area, such as electrical engineering, may end up doing on-the-job training in other aspects of mechatronics, or trying to learn how to incorporate components from an unfamiliar manufacturer.
One effective approach is to use the services of an integrator who specializes in mechatronics and is experienced in blending mechanics and electronics. Cross-disciplinary integrators are becoming more common as mechatronics applications expand, and the trend toward cross-disciplinary integration skill is consistent with the current industry focus on accomplishing more with fewer people.
Integration can act as a “force multiplier,” extending the capabilities of existing technology to create quantum leaps in production efficiency, reduced downtime, and cost savings. For example, an automotive production line can be made many times more productive by substituting different control commands for retooling, and an outboard support axis added to a 3-axis Cartesian robot creates a gantry device. Many similar solutions are possible for designers who adopt a multidisciplinary, full-system approach.
Use of 3D simulation during the design phase of the project can prevent the need for reconfiguring system elements later in the project.
After integration, the final step is implementation. But the final step should be well planned early in the process, or the result can be significant delays and added machine or production line costs. Avoid potential problems by clearly defining the roles and responsibilities of integrator and customer. This task can be a challenge in a process that blends a number of different engineering disciplines to create an integrated solution. The key is communication, right from the beginning — including detailed questions. For example, regarding system adjustments or changes, what is the responsibility of the integrator and what can be done by on-site personnel? The answers should be carefully documented to head off potential problems before they start. Of course, no one can foresee the future. But good implementation envisions the context in which a mechatronics system will operate.
Cross-disciplinary integrators are becoming more common as mechatronics applications expand.
As a cross-disciplinary process, mechatronics demands integrated thinking to go with integrated engineering. Part of this thinking involves the ability to envision the day-to-day operation of assembly line functions, including the working environment and the blending of electronic protocols, to anticipate and head off potential disciplines. Be prepared for the reality of cross-disciplinary requirements that may call for an integration specialist to get all the components working together. Finally, to implement the system, clearly communicate with everyone involved about their roles and responsibilities. For mechatronics to be truly successful, the development process must involve not only mechanical and electronic elements, but process elements as well: the key phases of design, integration, and implementation.
Software tools speed integration
Proper design begins with determining mathematical factors such as payload, travel distance, desired speed, and sizing of axes. Bosch Rexroth developed “LOSTPED”—a multi-step analysis process to help designers gather information for specifications.
To help answer mechatronic questions, Bosch Rexroth developed “LOSTPED”—a multi-step analysis process for gathering information for specifications. LOSTPED stands for Load (the weight or force applied), Orientation (direction each axis is mounted), Speed (and acceleration), Travel (distance and range of motion), Precision (repeatability or positioning accuracy), Environment (operating conditions), and Duty cycle (duration the machine will run; example: 24 hr/day, 5 days per week). In an automotive assembly application, for example, duty cycle and assembly line speed are crucial to determine insertion arm size, motor size and logic control, along with many other key factors.